A grave commitment that may turn out to be real fun (7)
I believe the answer is:
funeral
'a grave commitment that may turn' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'out to be real fun' is the wordplay.
'out to' is an anagram indicator.
'real'+'fun'='realfun'
'realfun' with letters rearranged gives 'FUNERAL'.
Can you help me to learn more?
(Other definitions for funeral that I've seen before include "Burial service" , "Obsequies" , "Burial ceremony" , "Burial rite" , "Sepulture" .)